Well actually, you only have up to your skirmish mission cap to lose...

Instead of give the scums free kills, you send your ship i and concentrate your attack on his expensive ship, bring a few down as you go...

Then you hyperdrove out when you have most nothing on the map (except maybe that little s-foiled xwing and stuff at the far corner)

Don't ever give the scums free things, make them pay with every bit of their blood.

I think this is debatable. If you are loosing big time, it really doesn't matter if you "make them pay" before being destroyed. You might get through the shields of a capital ship and damage it a little, or shoot down a few squardron of starfighters, but really, it won't matter that much in the end.

My point is, if you are loosing to the point when you consider retreating, your forces will get wipped out before they can cause any real damage.